Decision-directed control circuit

Abstract

An improved decision-directed control circuit is disclosed which supplies adjustments to adaptive circuitry in a communications system. The improvement is achieved by only supplying adjustments when there is a high probability that the adjustment is correct. In the disclosed embodiments, this high probability equates, at a minimum, to times when the adaptive circuit output has an amplitude which lies outside of a range extending from the largest to the smallest value of the digital signal. This adjustment approach can be used to adjust a variety of adaptive circuits including transversal equalizers, timing recovery circuits, cross-polarization cancellers and carrier recovery circuits.

What is claimed is: 
     
       1. Decision-directed control apparatus for use in a communications signal receiver wherein each received signal conveys information on a plurality of discrete signal levels, said apparatus comprising adjustable means for processing each received signal to form an associated first output signal;   means for determining when the amplitude of each first output signal in a predetermined group, comprising at least one preselected first output signal, lies outside of a range extending from a largest to a smallest of said signal levels; and   means responsive to said determining means for supplying adjustments to said processing means if the amplitude of each first output signal in said group lies outside of said range and supplying no adjustments if the amplitude of each first output signal in said group lies within said range, said adjustments altering the signal processing provided by said processing means.   
     
     
       2. The apparatus of claim 1 wherein said determining means determines when the amplitude of each first output signal in said group lies outside an associated subset of said range and supplies this determination to said supplying means. 
     
     
       3. The apparatus of claim 2 wherein said supplying means supplies adjustments if the amplitude of each first output signal in said group lies outside of said range at first times and the amplitude of each first output signal in said group lies outside said subset at second times. 
     
     
       4. The apparatus of claim 1 wherein said supplying means supplies adjustments formed in accordance with a least mean square algorithm. 
     
     
       5. The apparatus of claim 1 wherein said supplying means supplies adjustments formed in accordance with a zero forcing algorithm. 
     
     
       6. The apparatus of claim 1 wherein said processing means delivers a second output signal associated with each received signal to said determining means. 
     
     
       7. The apparatus of claim 6 wherein said determining means determines when the amplitude of each second output signal in said predetermined group, comprising at least one second output signal, lies outside an associated subset of said range and supplies this determination to said supplying means. 
     
     
       8. The apparatus of claim 7 wherein said supplying means supplies adjustments to said processing means if the amplitude of each first output signal in said predetermined group lies outside said range at first times and the amplitude of each second output signal in said predetermined group lies outside said subset at second times. 
     
     
       9. The apparatus of claim 1 wherein said processing means includes a transversal equalizer which is supplied with adjustments by said supplying means. 
     
     
       10. The apparatus of claim 1 wherein said processing means includes a cross polarization canceller which is supplied with adjustments by said supplying means. 
     
     
       11. The apparatus of claim 1 wherein said processing means includes a timing recovery circuit which is supplied with adjustments by said supplying means. 
     
     
       12. The apparatus of claim 1 wherein said processing means includes a carrier recovery circuit which is supplied with adjustments by said supplying means. 
     
     
       13. The apparatus of claim 1 wherein each first output signal in said predetermined group varies with the signal processing adjustments. 
     
     
       14. The apparatus of claim 7 wherein each second output signal in said predetermined group varies with the signal processing adjustments. 
     
     
       15. A method of adjusting decision-directed apparatus for use in a communications signal receiver wherein each received signal coveys information on a plurality of discrete signal levels, said method comprising the steps of processing each received signal to form an associated first output signal;   determining when the amplitude of each first output signal in a predetermined group, comprising at least one first output signal, lies outside of a range extending from a largest to a smallest of said signal levels; and   supplying adjustments which alter the processing provided to said received signal by said processing step if the amplitude of each first output signal in said group lies outside of said range and supplying no adjustments to said processing step if the amplitude of each first output signal in said group lies within said range.   
     
     
       16. The method of claim 15 further comprising the steps of determining when the amplitude of each first output signal in said group lies outside an associated subset of said range and supplying this determination to said supplying step.   
     
     
       17. The method of claim 16 wherein said supplying step supplies adjustments which alter the processing provided to said received signal by said processing step if the amplitude of each first output signal in said group lies outside of said range at first times and the amplitude of each first output second in said group lies outside of said subset at second times. 
     
     
       18. The method of claim 15 wherein said supplying step supplies adjustments formed in accordance with a least mean square algorithm. 
     
     
       19. The method of claim 15 wherein said supplying step supplies adjustments formed in accordance with a zero forcing algorithm. 
     
     
       20. The method of claim 15 wherein said processing step provides a second output siganl associated with each received signal to said determining step. 
     
     
       21. The method of claim 20 wherein said determining step determines when the amplitude of each second output signal in said predetermined group, comprising at least one second output signal, lies outside an associated subset of said range and supplies this determination to said supplying step. 
     
     
       22. The method of claim 21 wherein said supplying step supplies adjustments which alter the processing provided to said received signal by said processing step if the amplitude of each first output signal in said predetermined group lies outside said range at first times and the amplitude of each second output signal in said predetermined group lies outside said subset at second times. 
     
     
       23. The method of claim 15 wherein said processing of said received signal utilizes a transversal equalizer which is supplied with adjustments by said supplying step. 
     
     
       24. The method of claim 15 wherein said processing of said received signal includes a cross polarization canceller which is supplied with adjustments by said supplying step. 
     
     
       25. The method of claim 15 wherein said processing of said received signal includes a timing recovery circuit which is supplied with adjustments by said supplying step. 
     
     
       26. The method of claim 15 wherein said processing of said received signal includes a carrier recovery circuit which is supplied with adjsutments by said supplying step. 
     
     
       27. The method of claim 15 wherein each first output signal in said predetermined group varies with the adjustments provided to said processing step. 
     
     
       28. The method of claim 21 wherein each second output signal in said predetermined group varies with the adjustments provided to said processing step.